1. Field of the Invention
The present invention relates to an apparatus and method for measuring biological information and, more particularly, to an apparatus and method for precisely measuring various biological information by using a single measuring apparatus.
2. Description of the Related Art
As the people are becoming more interested in their health, many devices have been developed to allow users to obtain basic information related to various biological measurements through a simple operation at home. For example, mobile diagnosing devices have been developed and actively used to allow user to simply measure values of body fat, pulse, blood pressure, blood sugar, etc. at home without having to see a doctor.
The body mass index (BMI) denotes an amount of fat within a human body and is used as a major index for determining obesity. Among methods for measuring the body fat, a bio-electrical impedance measuring method and a near-infrared ray interactance optical method use a device.
The bioelectrical impedance measuring method measures the electrical impedance of the human body by applying a small current to the human body. That is, in this method, a ratio of the lean and fat body compositions is measured by using the characteristics that lean and fat compositions of the body have a different electrical resistance value.
In the near-infrared interactance optical method, by using the characteristics that lean and fat compositions of the body each absorbs light of a specific wavelength of a near infrared red region, the amount of light absorption that each composition absorbs or a transmission amount of light is measured and accordingly a ratio of the body compositions is calculated.
The bioelectrical impedance method had been developed a long time ago and frequently used traditionally with high precision, but because it is expensive and its measurement time is long, recently, the near-infrared interactance optical method which is relatively low-priced with short measurement time is increasingly used.
Although the precision of the near-infrared interactance optical method is inferior and a standardization operation must be performed before measurement, a measurement device of the optical method has been improved to have similar precision to that of the bioelectrical impedance method in line with the development of the optical technologies.
In the near-infrared interactance optical method, an absorption amount of infrared rays of each wavelength is relatively compared by using a plurality of infrared wavelengths according to each wavelength where an infrared absorption peak of each body composition appears. And it is compared with a measurement value of a standard test sample to show a ratio of each body composition.
However, the absorption peaks of each body composition, for example, an absorption peak of fat is 930 nm, moisture is 970 nm, and protein is 910 nm and 1020 nm, etc. are quite similar. In this respect, it is very difficult to fabricate an infrared light source such that infrared rays of a wavelength corresponding to their current peak positions are accurately radiated and bandwidths do not overlap.
In addition, because the plurality of infrared wavelengths are used, a signal processing circuit is complicated and a size and cost of a product increase.
FIG. 1 is a graph showing absorption of each wavelength of infrared radiation and FIG. 2 is a graph showing a relationship between the infrared absorbance and the body fat.
With reference to FIGS. 1 and 2, it is noted that an absorption amount of oil is smaller than that of other material over the full wavelength band (refer to FIG. 1). For a person with more muscle (comprising water by more than 70%) and less fat, infrared rays can hardy transmit therethrough, and for a person with less muscle and more fat, infrared rays can easily transmit therethrough.
Accordingly, by using a sample of a body whose body fat is known, a relationship between the body fat and the infrared absorbance can be obtained and expressed by the equation shown below (refer to FIG. 2):Body fat=K0+K1(log1/l)+K2(W/100)+K3(H/100)+K4(S)+K5(EL)wherein K0, K1, K2, K3, K4 and K5 respectively indicate proportional constants, ‘I’ indicates the infrared absorbance, ‘W’ indicates weight, ‘H’ indicates height, ‘S’ indicates gender and ‘EL’ indicates an exercise level.
The above equation also shows that the body fat has a relationship with the age, weight, height, gender and quantity of motion in addition to the infrared absorbance, and a ratio of body fat can be reversely calculated by measuring the infrared absorbance based on the formula.
There have been developed several methods for measuring the pulse (heart rate) of the human body, and among them, the optical method using the near infrared rays is the most suitable in consideration of user convenience, cost and portability. The principle of measuring pulse by the optical method will now be described with reference to FIG. 3.
FIG. 3 is a graph showing a change in the infrared absorbance according to each pulse period. As shown, when the amount of component of blood in a capillary that is periodically changed according to the heart rate by using the blood component of a blood vessel and an absorption spectrum of the infrared light of a particular wavelength is measured, the infrared absorbance also periodically changes, so the pulse can be measured by counting the period.
In addition, a degree of elasticity and aging of the blood vessel can be recognized by using the signals obtained by optically measuring the pulse signal.
The measured pulse signal as shown in FIG. 3 is differentiated to obtain a signal as shown in FIG. 4A, which is called an accelerated plethymogram signal.
Each peak of the accelerated plethymogram signal has meaningful information regarding a blood vessel and the heart. Accordingly, by scoring the size of each peak and waveforms by using a certain formula, and classifying the scores by stages, elasticity and aging state of the blood vessel can be known according to a shape of the accelerated plethymogram signal.
The formula used for classifying by stages can be expressed as follows:Score=(−b+c+d)/a (a, b, c, d=size of each peak of the accelerated plethymogram signal).
The waveforms classified into A to G by scoring according to the formula are as shown in FIG. 4B.
However, in case of the optical body fat measurement device, the optical pulse measurement device and a blood vessel elasticity measurement device using the same, although they use the infrared rays, because they use mutually different infrared wavelengths, it is difficult to implement both the body fat and pulse measurement function and the blood vessel elasticity measurement function in a single device.